With continuous development of communications technologies, communications terminals need to support more frequency bands. Here, the communications terminal may be a mobile phone, a data card, or another communications terminal. A communications terminal operating on different networks or in different frequency bands needs to select and switch a frequency band.
An existing communications terminal, when operating, is mainly controlled by chips, such as a transceiving chip. Some pins on these chips may indicate operating frequency bands of the communications terminal. This means that each pin represents a different operating frequency band of the communications terminal. That is, in an integrated circuit of a chip, a capacitive switch is arranged for a pin that corresponds to each operating frequency band of the terminal, and a direct-current signal input from the integrated control circuit is used as a logic level signal, so as to control an on/off state of the capacitive switch to select and switch a frequency band for the communications terminal. A conventional capacitive switch is made by using a micro-electro-mechanical systems MEMS (Micro-Electro-Mechanical Systems) technology, and transmission and cutoff of a signal are controlled by using the direct-current signal that is input from the integrated control circuit as an on/off state control signal of the capacitive switch. That is, when power is supplied to capacitive switches, input signals exist on all of pins that control multiple frequency bands, and a pin that corresponds to each frequency band is connected to a capacitive switch; when the terminal is operating in a certain frequency band, the direct-current signal that is input from the integrated control circuit and driven by a high voltage is sent to control ends of capacitive switches that are connected to pins indicating the other frequency bands; and this direct-current signal controls these capacitive switches to get disconnected, and then a signal input at an input end is cut off. Therefore, a frequency band is selected and switched in this process.
When a conventional capacitive switch selects a frequency band, however, a stress generated by a metal film bridge often cannot be released due to integrity of a double-clamped beam. As a result, the beam bulges or sinks, further causing a poor contact between the beam and a conducting layer. Then in a process of signal transmission, signal leakage often occurs due to the poor contact, thereby causing poor signal transmission quality of the communications terminal.